1. Technical Field
The present invention relates to an electrophoretic composition, a microcapsule and an electrophoretic display device.
2. Description of the Related Art
In recent years, in the advanced information society due to development of, for example, internet, cellular phones, and interactive televisions, needs for high quality thin display devices which require less consumption power have been growing. Among these devices, liquid crystal display devices employ a displaying principle in which liquid crystal molecule alignment is electrically controlled whereby to change optical characteristics is employed. In this situation, liquid crystal display devices have been actively researched and developed as display devices which can address the needs, and have been commercialized.
However, in most of liquid crystal display devices, transmission of light entered to the liquid crystal from a light source (back light) disposed at the back side is controlled, whereby images are displayed. Accordingly, in a well-lighted area, there is difficulty in viewing the images. Further, since it is necessary to always keep the light on, satisfactorily less power consumption is also an issue.
Studies on display devices to solve these issues have been actively made. For example, electrophoretic display devices are known (see, for example, Examined Japanese Published Examined Application Nos. 50-15115 and 50-15119). Such electrophoretic display devices include a pair of substrates which are disposed to have a gap therebetween and each substrate of the pair of substrate has an electrode that is an electrically conductive layer, the electrically conductive layer on at least one of the substrates being transparent. In the gap between the substrates, many charged and colored electrophoretic particles and a dispersion medium which has a different color from that of the electrophoretic particles are placed. Alternatively, there are devices in which two or more kinds of electrophoretic particles which are different from one another in a charged polarity and/or color, and a colorless dispersion medium are placed between the two substrates.
In such electrophoretic display devices, when negative voltage is applied to one electrode and positive voltage is applied to the other electrode, positively charged electrophoretic particles move toward the negative electrode so as to coat the negative electrode. When viewing the display device from the negative electrode side, the color of the electrophoretic particles can be seen. When the voltage applied to each of the electrodes is reversed, the color of the colored dispersion medium or another kind of electrophoretic particles can be seen. When such a voltage driving is carried out on a pixel basis of a number of arranged pixels, any images and characters can be displayed.
A study on the color display using a transparent colored-dispersion medium obtained by adding a dye to a dispersant has been carried out (for example, Japanese Application National Phase Publication No. 2010-525122 and International Publication WO 2005/017046 A2).
In the field of thermal lithographic offset printing, an overcoat composition including a water-soluble polymer dye having an absorption band of from 300 nm to 600 nm has been disclosed (see, for example, Japanese Application National Phase Publication No. 2010-534746).